42 Vol. XLin., Art. 5.— T. Katô: 



an optically negative character along the longer zone, the greatest 

 elasticity-axis existing along the longer axis. Refraction is always 

 a little higher than that of Canada balsarn. It is Si02 in chemical 

 composition. These properties correspond exactly with those of 

 chalcedony. The third crust is represented again by a quartz 

 layer, which is the last zonal precipitation in the stage of ring- ore 

 formation. Occasionally, if not always, a second cassiterite -bearing 

 band, maeroscopically an insignificant dark streak, is developed 

 concentrically in the last quartz crust (PI. Y., Fig. 2). Rarely, 

 however, is this band represented by a thick cassiterite layer, in 

 which case the ring-ore contains two concentric cassiterite layers. 

 This quartz zone is characterized by numerous small drusy cavities 

 lined with small crystals of quartz, which are sometimes encrusted 

 with fine crystals (cubes) of colourless or light purple fluorspar, 

 pyramidal crystals of light brown scheelite, and minute crystals of 

 siderite. 



Zincblende sometimes plays an important rôle in the formation 

 of the ring-ore. Exceedingly silicified rock- fragments are occasional- 

 ly encrusted with a zincblende layer, a few millimeters thick, and sub- 

 sequently covered successively by the quartz- cassiterite, chalcedony 

 and other layers. In places the nucleus of the ring -ore has been, 

 heavily impregnated with, or entirely replaced by, zincblende. 

 Chalcopyrite and bornite play also a significant part in the ring-ore. 

 They occur as an admixture in the cassiterite-bearing crust com- 

 monly in the form of small specks, or sometimes are deposited 

 directly on the nuclear rock- fragment. Frequently they are scat- 

 tered in the form of minute grains and streaks through the silicified 

 rock- fragment. It is certain that at an early epoch of the ring-ore 

 formation small quantities of zincblende, chalcopyrite and bornite 

 have been deposited from the vein-forming solutions, the cupriferous 



